Group iMessage Opt-out option?

My slo-pitch team's manager has created a group iMessage thread that has started to get out of control (100s of texts daily). How can we opt-out of this specific thread without having to turn iMessage off completely?

I used to be a BB user (mostly cause of BBM) but have switched over to iPhone, knowing Apple has iMessage (which is very similar to BBM). If my only option is to turn iMessage off completely, I'd rather not have an iPhone (it's that simple) and get a new Android.